Silicon ingot

ABSTRACT

A silicon ingot has opposite ends. A specific resistance, measured along an axis between the opposite ends of the silicon ingot, has at least one point of inflection where a concavity of the specific resistance changes along the axis. According to another embodiment, a silicon ingot has a first ingot part and a second ingot part between opposite ends of the silicon ingot. The first ingot part has a different specific resistance than the second ingot part. In a region of the silicon ingot between the first and second ingot parts, the specific resistance has at least one point of inflection where a concavity of the specific resistance changes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No.: 14/535,416 filed Nov. 7, 2014, now issued as U.S.Pat. No. 10,337,117 B2. The disclosures of all the above referencedpatent applications are incorporated herein by reference in theirentirety.

BACKGROUND

Silicon wafers grown by the Czochralski (CZ) method, e.g., by thestandard CZ method or by the magnetic CZ (MCZ) method or by theContinuous CZ (CCZ) method serve as a base material for manufacturing avariety of semiconductor devices and integrated circuits such as powersemiconductor devices and solar cells. In the Czochralski method,silicon is heated in a crucible to the melting point of silicon ataround 1416° C. to produce a melt of silicon. A small silicon seedcrystal is brought in contact with the melt. Molten silicon freezes onthe silicon seed crystal. By slowly pulling the silicon seed crystalaway from the melt, a crystalline silicon ingot is grown with a diameterin the range of one or several 100 mm and a length in the range of ameter or more. In the MCZ method, additionally an external magneticfield is applied to reduce an oxygen contamination level.

Growing of silicon with defined doping by the Czochralski method iscomplicated by segregation effects. The segregation coefficient of adopant material characterizes the relation between the concentration ofthe dopant material in the growing crystal and that of the melt.Typically, dopant materials have segregation coefficients lower than onemeaning that the solubility of the dopant material in the melt is largerthan in the solid. This typically leads to an increase of dopingconcentration in the ingot with increasing distance from the seedcrystal.

Since in Czochralski grown silicon ingots, depending upon application ofthe grown silicon, a tolerance range of doping concentration or specificresistance along the axial direction between opposite ends of thesilicon ingot may be smaller than the variability of dopingconcentration or specific resistance caused by segregation effectsduring CZ growth, different parts of the silicon ingot may be used asbase materials having different target doping concentrations withoverlapping, adjoining or spaced apart tolerance ranges of dopingconcentration or specific resistance. Such a partitioning of the siliconingot is also known as order matching.

It is desirable to provide a silicon ingot and a method of manufacturinga silicon ingot grown by the Czochralski method enabling an improvedyield with respect to silicon ingot parts having doping concentrationsor specific resistances lying in acceptable tolerance ranges.

SUMMARY

According to an embodiment, a method of Czochralski growth of a siliconingot is disclosed. The method comprises melting a mixture of siliconmaterial and an n-type dopant material in a crucible. The silicon ingotis extracted from the molten silicon during an extraction time period.The method further comprises doping the silicon ingot with additionaln-type dopant material during at least one sub-period of the extractiontime period.

According to an embodiment, an n-doped silicon ingot is disclosed. Aspecific resistance p of then-doped silicon ingot, along an axis betweenopposite ends of the silicon ingot, has at least one point of inflectionwhere a concavity of the specific resistance p changes along the axis.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description and onviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification. The drawings illustrate the embodiments ofthe present disclosure and together with the description serve toexplain principles of the disclosure. Other embodiments and intendedadvantages will be readily appreciated as they become better understoodby reference to the following detailed description.

FIG. 1 is a schematic flow chart for illustrating a method ofmanufacturing an n-type silicon ingot.

FIG. 2 is a graph illustrating a specific resistance p versus an axialdirection a of a silicon ingot grown by the method of FIG. 1.

FIG. 3 is a schematic cross-sectional view of a CZ growth system forcarrying out the method illustrated in FIG. 1.

FIG. 4 is a schematic cross-sectional view of a crucible forillustrating a method of doping the crucible with dopant material.

FIG. 5 is a schematic cross-sectional view of a part of a CZ growthsystem for illustrating a method of adding dopants to a silicon melt inthe crucible.

FIG. 6 is a graph illustrating a simulated concentration ofnon-compensated phosphorus along an axial position of a CZ grown siliconingot with respect to different ratios of boron and phosphorus added tothe silicon melt.

FIG. 7 is a graph illustrating a simulated specific resistance along anaxial position of a CZ grown silicon ingot with respect to differentratios of boron and phosphorus added to the silicon melt.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which are shownby way of illustrations specific embodiments in which the disclosure maybe practiced. It is to be understood that other embodiments may beutilized and structural or logical changes may be made without departingfrom the scope of the present invention. For example, featuresillustrated or described for one embodiment can be used on or inconjunction with other embodiments to yield yet a further embodiment. Itis intended that the present disclosure includes such modifications andvariations. The examples are described using specific language thatshould not be construed as limiting the scope of the appending claims.The drawings are not scaled and are for illustrative purposes only. Forclarity, the same elements have been designated by correspondingreferences in the different drawings if not stated otherwise.

The terms “having,” “containing,” “including,” “comprising” and the likeare open and the terms indicate the presence of stated structures,elements or features but not preclude the presence of additionalelements or features. The articles “a,” “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

The term “electrically connected” describes a permanent low-ohmicconnection between electrically connected elements, for example a directcontact between the concerned elements or a low-ohmic connection via ametal and/or highly doped semiconductor. The term “electrically coupled”includes that one or more intervening element(s) adapted for signaltransmission may exist between the electrically coupled elements, forexample elements that temporarily provide a low-ohmic connection in afirst state and a high-ohmic electric decoupling in a second state.

The Figures illustrate relative doping concentrations by indicating “−”or “+” next to the doping type “n” or “p”. For example, “n” means adoping concentration that is lower than the doping concentration of an“n”-doping region while an “n”-doping region has a higher dopingconcentration than an “n”-doping region. Doping regions of the samerelative doping concentration do not necessarily have the same absolutedoping concentration. For example, two different “n”-doping regions mayhave the same or different absolute doping concentrations.

FIG. 1 refers to a method of manufacturing a silicon ingot.

Process feature S100 of the method includes melting a mixture of siliconmaterial and an n-type dopant material in a crucible.

Process feature S110 of the method includes extracting the silicon ingotfrom the molten silicon over an extraction time period.

Process feature S120 of the method includes doping the silicon ingotwith additional n-type dopant material during at least one sub-period ofthe extraction time period.

By doping the silicon ingot with the additional n-type dopant materialduring at least one sub-period of the extraction time period,manufacturing of at least two ingot parts having different targetspecifications of specific resistance p, also known as order matching,can be improved as is illustrated in the schematic graph of FIG. 2. Theschematic graph of FIG. 2 illustrates a specific resistance p of asilicon ingot versus an axial direction a. Growth of the silicon ingotstarted at the axial position 0%. Due to segregation effects duringgrowth of the n-type silicon ingot, a negative slope of the specificresistance increases toward and end of the silicon ingot. By temporarydoping with the additional n-type dopant material after growth of afirst silicon ingot part P1 fulfilling a first target specification ofspecific resistance, an axial distance da between the first siliconingot part P1 and a second silicon ingot part P2 fulfilling a differenttarget specification of specific resistance can be decreased comparedwith a second reference ingot part P2 REF grown without doping with theadditional n-type dopant material. The temporary doping with theadditional n-type dopant material leads to an increase of the negativeslope of the specific resistance along an axial direction of the siliconingot. By carrying out the doping with the additional n-type dopantmaterial in a specific resistance range Δρ1 between the first and secondtarget specifications, an axial distance da between the first and secondsilicon ingot parts P1, P2 fulfilling the first and second targetspecifications can be shortened compared to an axial distance darefbetween the first ingot part P1 and the second reference ingot partP2REF. In other words, the second silicon ingot part P2 is shiftedtoward an origin of the silicon ingot, Since the negative slope of thespecific resistance ρ decreases along the axial direction a toward theorigin of the silicon ingot due to segregation effects, an extension ofthe second silicon ingot part P2 fulfilling the second targetspecification can be increased compared to the second reference ingotpart P2REF, thereby improving the yield.

According to an embodiment, the additional n-type dopant material isphosphorus.

According to another embodiment, the silicon ingot is doped with theadditional n-type dopant material by a vapor phase doping technique. Anembodiment includes controlling inlet of a dopant precursor gas into areaction chamber including the silicon ingot. Phosphine (PH₃) and arsine(AsH₃) are examples for precursor gases for n-type doping of silicon.

According to another embodiment, doping the silicon ingot with theadditional n-type dopant material includes melting an n-type dopantsource material in the crucible. The silicon ingot may be doped with theadditional n-type dopant material by adjusting a depth of the n-typedopant source material into the molten silicon, the n-type dopant sourcematerial including the additional n-type dopant material. Adjusting thedepth of the n-type dopant source material dipped into the moltensilicon in the crucible may include measuring a weight of the n-typedopant source material.

According to another embodiment, the n-type dopant source material is inthe shape of one or more rods. The one or more rods may be dipped intothe silicon melt by a puller mechanism. The puller mechanism holds then-type dopant source material, dips the n-type dopant source materialinto the silicon melt and also pulls the dopant source material out ofthe silicon melt. A control mechanism is configured to control thepuller mechanism. The control mechanism may control the puller mechanismby wired or wireless control signal transmission, for example.

According to an embodiment, the n-type dopant source material is made ofquartz or silicon carbide doped with the additional n-type dopantmaterial. A concentration profile of the additional n-type dopantmaterial into a depth of the n-type dopant source material may have apeak below a surface of the n-type dopant source material. Introducingthe n-type dopant material into the n-type dopant source material may becarried out by at least one of the processes in-situ doping, plasmadeposition through a surface of the n-type dopant source material, ionimplantation through the surface of the n-type dopant source materialand diffusion through the surface of the n-type dopant source material.Adding the n-type dopant source material having a peak below a surfaceof the n-type dopant source material leads to a delay in addingadditional n-type dopants to the melt depending on a depth profile ofdoping and a melting rate of the n-type dopant source material.

According to an embodiment, a degree of doping the silicon ingot withthe additional n-type dopant material during the extraction time periodis varied between no doping and maximum doping. Doping of the siliconingot with the additional n-type dopant material may be suppressed bystopping additional n-type dopants entering the molten silicon, forexample by moving out the n-type dopant source material, e.g., a rodfrom the molten silicon via the puller mechanism or by stopping inlet ofthe dopant precursor gas into the reaction chamber including the siliconingot.

According to an embodiment, a net n-type doping in the silicon ingot isset between 1×10¹³ cm⁻³ and 1×10¹⁵ cm⁻³. Raw material, for examplewafers for power semiconductors such as IGBTs, diodes, insulated gatefield effect transistors (IGFETs) and thyristors may have a net n-typedoping range between 1×10¹³ cm⁻³ and 1×10¹⁵ cm⁻³, for example.

According to another embodiment, the silicon ingot is doped with p-typedopant material by adding the p-type dopant material to the silicon meltvia at least one of a p-type dopant source material or by a vapor phasedoping technique. According to an embodiment, the p-type dopant materialis one of boron, aluminum and gallium. Doping with p-type dopantmaterial leads to a partial compensation of the n-type doping. Due todifferent segregation of the n- and p-type dopants, a further decreaseof the negative slope of specific resistance along the axial direction acan be achieved. When adding the p-type dopants in a growth period ofthe first and second ingot parts P1, P2, the negative slope decreasefalls within these periods. Thereby, an extension of the first andsecond ingot parts P1, P2 along the axial direction a can be increased,leading to an improved yield. Since the method described above allowsfor a shift of silicon ingot parts of specified specific resistancealong the axial direction, other characteristics of silicon ingot partsvarying along the axial direction, for example oxygen content, may beadjusted by appropriately shifting the target silicon ingot parts alongthe axial direction.

According to an embodiment, the silicon ingot is doped with the p-typedopant material by a vapor phase doping technique.

According to another embodiment, doping the silicon ingot with thep-type dopant material includes melting a p-type dopant source materialin the crucible. The silicon ingot may be doped with the p-type dopantmaterial by adjusting a depth of the p-type dopant source material intothe molten silicon, the p-type dopant source material including thep-type dopant material. Adjusting the depth of the p-type dopant sourcematerial dipped into the molten silicon in the crucible may includemeasuring a weight of the p-type dopant source material. The p-typedopant source material may be in the shape of one or more rods. Thep-type dopant source material may be made of quartz or silicon carbidedoped with the additional n-type dopant material. A concentrationprofile of the p-type dopant material into a depth of the p-type dopantsource material may have a peak below a surface of the p-type dopantsource material. The p-type dopant material may be introduced into thep-type dopant source material by at least one of the processes in-situdoping, plasma deposition through a surface of the p-type dopant sourcematerial, ion implantation through the surface of the p-type dopantsource material and diffusion through the surface of the p-type dopantsource material. A degree of doping the silicon ingot with theadditional n-type dopant material during the extraction time period maybe altered between no doping and maximum doping.

FIG. 3 is a simplified schematic cross-sectional view of a CZ growthsystem 100 for carrying out the method illustrated in FIG. 1.

The CZ growth system 100 includes a crucible 105, e.g., a quartzcrucible on a crucible support 106, e.g., a graphite susceptor. A heater107, e.g., a radio frequency (RF) coil surrounds the crucible. Theheater 107 may be arranged at lateral sides and/or at a bottom side ofthe crucible 105. The crucible 105 may be rotated by a supporting shaft108.

The mixture of silicon material, e.g., a non-crystalline raw materialsuch as polysilicon and an n-type dopant material such as phosphorus(P), antimony (Sb), arsenic (As) or any combination thereof is melted inthe crucible by heating via the heater 107. The n-type dopant materialmay already constitute or be part of the initial doping of the siliconmaterial to be melted and/or may be added as a solid, liquid or gaseousdopant source material. According to an embodiment, the solid dopantsource material is a dopant source particle such as a dopant sourcepill. The dopant source material may have a predetermined shape such asa disc shape, spherical shape or a cubic shape. By way of example, theshape of the dopant source material may be adapted to a supply device109 such as a dispenser configured to supply the dopant source materialto a silicon melt 110 in the crucible 105.

According to an embodiment, the dopant source material may include, inaddition to the dopant material, a carrier material or a bindermaterial. By way of example, the dopant source material may be quartz orsilicon carbide (SiC) doped with the dopant material. According toanother embodiment, the dopant source material may be a highly dopedsilicon material such as a highly doped polysilicon material that isdoped to a greater extent than the silicon raw material. According toyet another embodiment, the dopant source material may be boron nitrideand/or boron carbide.

A silicon ingot 112 is pulled out of the crucible 105 containing thesilicon melt 110 by dipping a seed crystal 114 into the silicon melt 110which is subsequently slowly withdrawn at a surface temperature of themelt just above the melting point of silicon. The seed crystal 114 is asingle crystalline silicon seed mounted on a seed support 115 rotated bya pull shaft 116. A pulling rate which typically is in a range of a fewmm/min and a temperature profile influence a diameter of the CZ grownsilicon ingot 112.

When extracting the silicon ingot 112 with the CZ growth system 100according to the method illustrated in FIG. 1, the additional n-typedopant material is added to the silicon melt during at least onesub-period of the extraction time.

According to an embodiment, the additional n-type dopant material istemporarily added to the molten silicon from a doped quartz materialsuch as a phosphorus doped quartz material supplied to the silicon melt110 by the supply device 109.

According to another embodiment, the additional n-type dopant materialis added to the silicon melt 100 from a doped crucible. The crucibledoped with additional n-type dopant material may be formed by implantingthe additional n-type dopant material, for example phosphorus into thecrucible, (cf. schematic cross-sectional view of FIG. 4). The additionaln-type dopant material may be implanted into the crucible 105 by one ormore tilted implants, cf. labels I₂ ² and I₃ ² and/or by non-tiltedimplant, cf. label I₁ ² in FIG. 4. A distribution of tilt angle(s) maybe used to adjust the amount of the additional n-type dopant materialthat is supplied to the silicon melt 110 by dissolving a material of thecrucible 105 in the silicon melt 110, e.g., at a rate in the range ofapproximately 10 μm/hour in case of a crucible made of quartz. Theadditional n-type dopant material may be implanted into the crucible atvarious energies and/or at various doses. Applying a thermal budget tothe crucible 105 by heating may allow for setting a retrograde profileof the additional n-type dopant material in the crucible 105. Multipleimplants at various energies and/or doses further allow for setting aprofile of the additional n-type dopant material into a depth of thecrucible 105. Thus, a rate of adding the additional n-type dopantmaterial into the silicon melt 110 may be adjusted, i.e. by selection ofimplantation parameters the rate of the addition of the additionaln-type dopant material can be varied and controlled in a well-definedmanner. By way of example, the profile of the additional n-type dopantmaterial in the crucible 105 may be a retrograde profile. As analternative or in addition to implanting the additional n-type dopantmaterial into the crucible 105, the additional n-type dopant materialmay also be introduced into the crucible 105 by another process, e.g.,by diffusion from a diffusion source such as a solid diffusion source ofthe additional n-type dopant material, for example. As a furtheralternative or in addition to the above processes of introducing theadditional n-type dopant material into the crucible 105, the additionaln-type dopant material may also be introduced into the crucible 105in-situ, i.e., during formation of the crucible 105.

According to yet another embodiment the additional n-type dopantmaterial may be introduced into the silicon melt 110 from the gas phase,e.g., by supply of phosphine (PH₃) as a precursor gas for n-type dopingof silicon via the supply device 109. According to an embodiment, supplyof boron in the gas phase may occur via a supply of inert gas into theCZ growth system 100. According to another embodiment, supply ofadditional n-type dopant material in the gas phase may occur via one ormore tubes, e.g., a quartz tube extending into the silicon melt 110.According to yet another embodiment, supply of the additional n-typedopant material in the gas phase may occur via one or more tubes endingat a short distance to the silicon melt 110. The tubes may include oneor more openings at an outlet, e.g., in the form of a showerhead, forexample.

According to another embodiment, a liner layer may be formed on thecrucible 105 for controlling diffusion of the additional n-type dopantmaterial out of the crucible 105 into the silicon melt 110. As anexample, the liner layer may be formed of quartz and/or silicon carbide.According to an embodiment, the liner layer may be dissolved in thesilicon melt 100 before the additional n-type dopant material includedin the crucible gets dissolved in the silicon melt 110 and serves as adopant during the growth process of the silicon ingot 112. This allowsfor adjusting a point of time when the additional n-type dopant materialis available in the silicon melt as a dopant to be introduced into thesilicon ingot 112. The liner layer may also delay introduction of theadditional n-type dopant material into the silicon melt 110 by a timeperiod that is required for diffusion of the additional n-type dopantmaterial from the crucible 105 through the liner layer and into thesilicon melt 110.

According to another embodiment, the method of manufacturing the siliconingot 112 further includes altering a rate of adding the additionaln-type dopant material to the silicon melt 110. According to anembodiment, altering the rate of adding the additional n-type dopantmaterial to the silicon melt 110 includes altering at least one of size,geometry, and rate of delivery of particles including the additionaln-type dopant material. By way of example, the rate may be increased byincreasing a diameter of the particles doped with the dopant material.As an additional or alternative measure, the rate of adding theadditional n-type dopant material to the silicon melt 110 may beincreased by increasing a speed of supplying the dopant source materialinto the silicon melt 110 by the supply device 109.

According to another embodiment illustrated in the schematiccross-sectional view of FIG. 5, altering the rate of adding theadditional n-type dopant material to the silicon melt 110 includesaltering a depth d of a dopant source material 125 dipped into thesilicon melt 110.

According to another embodiment, altering the rate of adding theadditional n-type dopant material to the silicon melt 110 includesaltering a temperature of the dopant source material 125. By way ofexample, by increasing a temperature of the dopant source material,e.g., by heating, the amount of the additional n-type dopant materialintroduced into the silicon melt 110 out of the dopant source material125 may be increased. The dopant source material 125 is doped with theadditional n-type dopant material. According to an embodiment, doping ofthe dopant source material is carried out by one of in-situ doping, by aplasma deposition process through a surface 126 of the dopant sourcematerial 125, by ion implantation through the surface 126 of the dopantsource material 125 and by a diffusion process through the surface 126of the dopant source material 125. The dopant source material 125 may beshaped as a bar, a cylinder, a cone or a pyramid, for example. Thedopant source material 125 may also be made of a plurality of separatedopant source pieces having one or a combination of different shapes.The depth d of a part of the dopant source material 125 that is dippedinto the silicon melt 110 may be changed by a puller mechanism 127. Thepuller mechanism 127 holds the dopant source material 125, dips thedopant source material 125 into the silicon melt 110 and also pulls thedopant source material 125 out of the silicon melt 110. A controlmechanism 128 is configured to control the puller mechanism 127. Thecontrol mechanism 128 may control the puller mechanism 127 by wired orwireless control signal transmission, for example.

According to another embodiment, altering the rate of adding theadditional n-type dopant material to the silicon melt 110 includesaltering a flow or partial pressure of a precursor gas, e.g., phosphine(PH₃) when doping the silicon melt 110 with boron from the gas phase.

The method for manufacturing the silicon ingot 112 described above leadsto an improved order matching of at least two ingot parts havingdifferent target specifications of specific resistance ρ.

Partial counter-doping with p-type dopant material may be carried out bysimilar techniques as described above with respect to additional n-typedoping. Doping with p-type dopant material leads to a partialcompensation of the n-type doping. Due to different segregation of then- and p-type dopants, a further decrease of the negative slope ofspecific resistance along the axial direction can be achieved. Whenadding the p-type dopants in a growth period of ingot parts falling intoa specified range of target specific resistance, an extension of theseingot parts along the axial direction can be increased, leading to animproved yield. Further details on decreasing the negative slope ofspecific resistance along the axial direction is given below.

An axial profile of doping caused by segregation of dopant materialduring CZ growth can be approximated by equation (1) below:

$\begin{matrix}{{c(p)} = {{k_{0}{c_{0}\left( {1 - p} \right)}^{k_{0} - 1}} + {F_{0}{\frac{k_{0}}{1 - k_{0}}\left\lbrack {\left( {1 - p} \right)^{k_{0} - 1} - 1} \right\rbrack}}}} & (1)\end{matrix}$

The first term in the equation (1) refers to a doping that has beenadded to the melt before extracting the silicon ingot from the melt.According to the above embodiments, a basic n-type dopant material maybe described by the first term of equation (1). The second term refersto adding dopant material at a constant rate into the melt during CZgrowth. According to the above embodiments, adding the boron or anotheradditional dopant material may be described by the second term ofequation (1).

In the above equation (1), c(p) denotes a concentration of the dopantmaterial in the silicon ingot (atoms/cm³), p denotes a portion of theinitial melt during CZ growth that has been crystallized and correspondsto an axial position between 0% and 100% of the completely grown siliconingot, k₀ denotes a segregation coefficient of the dopant material,e.g., approx. 0.8 for boron (B) in silicon and approx. 0.35 forphosphorus (P) in silicon, c₀ denotes an initial concentration of thedopant material in the melt (atoms/cm³) and F₀ denotes a total amount ofthe dopant material that is constantly (relative to the pulling rate)added to the melt divided by the initial volume of the melt (atoms/cm³).

FIG. 6 illustrates calculated concentrations of non-compensatedphosphorus (P), i.e., net n-doping versus an axial position betweenopposite ends of a silicon ingot. The illustrated curves refer todifferent ratios of boron (B) and phosphorus (P), i.e., F_(0B)/c_(0P)corresponding to the ratio of the total amount of boron that isconstantly (relative to the pulling rate) added to the silicon meltdivided by the initial volume of the melt (F_(0B) in atoms/cm³) and aninitial concentration of phosphorus in the melt (c_(0P) in atoms/cm³).

The illustrated curves refer to values of F_(0B)/c_(0P) of 0%, 10%, 20%,30%, 40%, 50%.

FIG. 7 illustrates calculated specific resistance curves versus an axialposition between opposite ends of a silicon ingot. Similar to theparameter curves illustrated in FIG. 6, the curves illustrated in FIG. 7refer to different ratios of boron (B) and phosphorus (P), i.e.,F_(0B)/c_(0P) corresponding to the ratio of the total amount of boronthat is constantly (relative to the pulling rate) added to the siliconmelt divided by the initial volume of the melt (F_(0B) in atoms/cm³) andan initial concentration of phosphorus in the melt (c_(0P) inatoms/cm³).

Similar to the parameter curves illustrated in FIG. 6, the curvesillustrated in FIG. 7 refer to values of F_(0B)/c_(0P) of 0%, 10%, 20%,30%, 40%, 50%. By adding boron to the melt during CZ growth and therebyadding a compensation dopant to the melt during the CZ growth, themethod described with reference to FIGS. 1 to 5 allows for a reductionof a negative slope of the specific resistance along the axial directionbetween opposite ends of the silicon ingot. Since use of silicon ingotsfor supplying wafers for manufacturing a semiconductor device mayrequire small tolerances with respect to the specific resistance, e.g.,for manufacturing of insulated gate bipolar transistors (IGBTs), forexample, the method described with reference to FIGS. 6 and 7 allows foryield improvement. An axial length PREF of a silicon ingot part withoutp-type counter-doping falling in a specific resistance range between p₁and p₂ is smaller than an axial length P a silicon ingot part with 10%p-type counter-doping falling in the specific resistance range betweenp₁ and p₂.

Based on the method illustrated and described with respect to FIGS. 1 to7, table 1 illustrates a maximum portion of the ingot along the axialdirection having a specific fluctuation of specific resistance and aspecific ratio of boron (B) and phosphorus (P), i.e. F_(0B)/c_(0P)corresponding to the ratio of the total amount of boron that isconstantly (relative to the pulling rate) added to the silicon meltdivided by the initial volume of the melt (F_(0B) in atoms/cm³) and aninitial concentration of phosphorus in the melt (c_(0P) in atoms/cm³).Table 1 refers to values of F_(0B)/c_(0P) of 0%, 10% , 20%, 30%, 40%,50%, and to axial fluctuations of the specific resistance of +/−5%,+/−10%, +/−15%, +/−20%, +/−30%, +/−50%. By adding boron to the meltduring CZ growth and thereby adding a compensation dopant to the meltduring the CZ growth, the method described with reference to FIGS. 1 to6 allows for a yield improvement by increasing the maximum portion ofthe ingot along the axial direction having a specific fluctuation ofspecific resistance. As an example, the axial portion of the ingothaving a fluctuation of specific resistance of +/−10% may be increasedfrom 26% (no compensation doping) to 78% (compensation dopingF_(0B)/c_(0P) of 40%).

TABLE 1 boron compensation flow/initial maximum ingot length doping withwith axial fluctuation of specific resistance of phosphorous +/− 5% +/−10% +/− 15% +/− 20% +/− 30% +/− 50% no 14% 26% 36% 46% 60% 80%compensation 20% 32% 48% 58% 66% 76% 88% 30% 56% 66% 74% 78% 84% 92% 35%66% 74% 78% 82% 86% 92% 40% 38% 78% 82% 84% 88% 92% 45% 22% 44% 84% 86%88% 94%

According to the method illustrated with respect to FIGS. 6 to 7, boronis constantly added (relative to the pulling rate) to the silicon melt(described by the term F_(0B) in atoms/cm³) and phosphorus is added asan initial concentration to the melt (described by the term cop inatoms/cm³). According to other embodiments, boron may be added to themelt at an altering rate. Apart from or in addition to phosphorus, theadditional n-type dopant material such as phosphorus, antimony orarsenic may added in ingot growth intervals between ingot parts fallinginto a specific target resistance as is illustrated and described withrespect to FIGS. 1 and 2, for example.

In addition to adding boron to the melt during CZ growth a part of theoverall boron may also be added to the melt before CZ growth which maybe described by a term cop in equation (1). Likewise, in addition toadding phosphorus or the another n-type dopant material as an initialconcentration to the melt, a part of the phosphorus or the additionaln-type dopant material may also be added to the melt during CZ growthwhich may be described by a term FOP in equation (1) in case ofconstantly adding the phosphorus or the other n-type dopant materialrelative to the pulling rate.

According to an embodiment of a silicon ingot, a specific resistance p,along an axis between opposite ends of the silicon ingot, has at leastone point of inflection POI where a concavity of the specific resistancep changes along the axis as is illustrated in the graph of FIG. 2.

According to an embodiment, a net n-type doping in the silicon ingot isbetween 1×10¹³ cm⁻³ and 1×10¹⁵ cm⁻³.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A silicon ingot, comprising a first ingot partand a second ingot part between opposite ends of the silicon ingot,wherein the first ingot part has a different specific resistance thanthe second ingot part, wherein in a region of the silicon ingot betweenthe first and second ingot parts, the specific resistance has at leastone point of inflection where a concavity of the specific resistancechanges, wherein the silicon ingot is doped with both p-type dopantmaterial and n-type dopant material, wherein the p-type dopant materialis at least one of boron, aluminum and gallium, and wherein the n-typedopant material is at least one of phosphorus, antimony and arsenic. 2.The silicon ingot of claim 1, wherein the first ingot part is disposedcloser to a first one of the ends at which growth of the silicon ingotbegan, wherein the second ingot part is disposed closer to a second oneof the ends at which growth of the silicon ingot ended.
 3. The siliconingot of claim 2, wherein the first ingot part has a higher specificresistance than the second ingot part.
 4. The silicon ingot of claim 2,wherein the specific resistance has a negative slope starting from thefirst one of the ends at which growth of the silicon ingot began to thesecond one of the ends end at which growth of the silicon ingot ended.5. The silicon ingot of claim 4, wherein the negative slope of thespecific resistance increases toward the second one of the ends at whichgrowth of the silicon ingot ended.
 6. The silicon ingot of claim 1,wherein the first ingot part is doped with the n-type dopant material,and wherein the region of the silicon ingot between the first and secondingot parts is doped with the n-type dopant material and additionaln-type dopant material so that the specific resistance in the region ofthe silicon ingot between the first and second ingot parts is higherthan the specific resistance in the first ingot part.
 7. The siliconingot of claim 1, wherein the silicon ingot has a net n-type doping in arange between 1×10¹³ cm ⁻³ and 1×10¹⁵ cm⁻³.
 8. The silicon ingot ofclaim 1, wherein the p-type dopant material partially compensates then-type doping.
 9. The silicon ingot of claim 1, wherein a degree ofdoping by the p-type dopant material varies between no doping andmaximum doping in the silicon ingot.
 10. The silicon ingot of claim 1,wherein the first and second ingot parts are each doped with the n-typedopant material and the p-type dopant material, and wherein the p-typedopant material partially compensates the n-type doping in the first andsecond ingot parts.